A GP has spoken out after being targeted with hate mail labelling her a “child murderer” by anti-vaccination campaigners.

Dr Preeya Alexander was last week called a “bad doctor” and a “killer” in messages from dozens of online trolls, in response to a post she had made on photo-sharing app Instagram about vaccination.

The Melbourne GP was pictured with her young daughter at her clinic shortly after receiving their flu shots. The post also included practical information about vaccine safety.

But in response, she was bombarded with abusive messages and threats, in what appeared to be a co-ordinated attack.